Leukonychia is the medical term for the white spots on your nails. The cause is actually mild injury, not lack of calcium or other vitamins as commonly believed. Injuries to the base of the nail are the most common cause of these spots, you may not even notice or feel the injury but you will see the results. These spots do not need to be treated and they will go away in a few weeks or months, whatever time it takes for your nail to grow out.
However, if your entire nail is becoming white, this could be a sign of a nutritional or other medical disorder so you should go to your doctor in this case.
Now go out there and protect your nails!